The Tecnifibre Black Code 4S tennis string is the official string of the ATP World Tour & this reel is 200m (660ft) long. This monofilament string is made from high-density polyester & has a square section made to provide a maximum level of spin. Thermocare technology keeps it highly flexible & tension maintenance is good. The string is black & gives users 20% more power than the Pro Red Code string & 15% more durability than the Black Code.